What settings to make so that two mail servers work?

Question

Mail server

There is a working postfix in freebsd.
Now I have launched Exchange Online for testing, connected the domain, started the user.
I registered mx-records in the DNS settings. The postfix has a weight of "5", for the MS server - the weight of "15"
Wrote a letter to the only user - the error "550 5.1.1: Recipient address rejected: User unknown in virtual mailbox table" was returned
That is, the poll of available users was not performed at all mail servers.
Tell me how to set up and is it possible?

Answer 1

http://www.postfix.org/postconf.5.html#luser_relay
luser_relay = [email protected]

Answer 2

550 5.1.1: Recipient address rejected: User unknown in virtual mailbox table

- Postfix answers you. If you use the same IP address for both mail servers, then one (in your case, most likely Postfix) of them should be a relay (mail forwarder) for the other, the DNS server functionality does not imply determining which of your MX records the letter is intended for. Here is a good manual that helped me set everything up in an identical situation: article

Answer 3

Two mx with different weights, in the same domain, can be done for fault tolerance purposes, and not for separating the processing of different mailboxes. The remote mailer will try to deliver the message to the server with the lowest priority, and if the server does not respond at all, or returns a temporary error, it will try to send via the backup MX.
But the "user not found" error indicates that the server is running, and there is no point in sending it to a spare.
luser_relay will not work for you, because "Note: luser_relay works only for the Postfix local(8) delivery agent. " and you are using a virtual transport, according to the error message.
You can make an additional transport that will forward letters for certain recipients to your second server, in principle.
But it seems to me that you want the wrong thing from the very beginning. =)
Either you need to make postfix a relay for the entire domain, or switch the maintenance of the entire domain to exchange.